fn main() {
    println!("{argument}", argument = "test"); // => "test"

    /* 填空 */
    assert_eq!(format!("{name}{}", 1, name = 2), "21");
    assert_eq!(format!("{a} {c} {b}", a = "a", b = 'b', c = 3), "a 3 b");

    /* 修复错误 */
    // 具名参数必须放在其它参数后面
    println!("{abc} {}", 2, abc = "def");

    println!("Success!")
}
